Dissable putty tabcompletion sound
When you start Putty, go under the Bell tab and configure it the way you wish
Save your session ;)
For additional information see http://kb.site5.com/shell-access-ssh/putty-how-to-change-the-bell-style-and-settings/ or the PuTTy documentation of your choice.
Open PuTTY, choose the session you want and click "load".
Now under Terminal, Bell choose:
None (bell disabled)
Return to session, and click "save".
Open your session and enjoy the silence.